1. Field of the Invention
The present invention relates generally to apparatus and methods for adjusting the intonation of a stringed instrument such as a guitar and for adjusting the output of individual strings of a stringed instrument utilizing an electrical pickup.
2. Description of the Prior Art
Traditional steel string acoustic guitars employ a bridge saddle which is slanted, i.e., not perpendicular to the instrument's center line, to provide intonation compensation. The larger bass strings require a longer length between the nut and bridge of the guitar than do the smaller treble strings, due to their increased mass and stretching characteristics. In order to play in tune, the instrument must have a slanted bridge saddle.
In theory, this works well enough, assuming the manufacturer has placed the saddle position correctly. However, string length for correct intonation is dependent on several factors including the mass of the string, the core wire diameter of the string, the instrument's action height, and scale length, to name several.
It can readily be seen that, of these several variables, the scale length is set by the factory, as is the basic position of the saddle. If the manufacturer has positioned the saddle correctly based on a certain set of strings, and if the player always uses only those strings, at the factory action height positions, he may reasonably hope the guitar will play in tune. Quite often, of course, the guitar does not play satisfactorily in tune. This leads to repairs or modifications at custom guitar repair shops which alter the intonation of the individual strings by filing the top edge of the bridge saddle to move the location of the supporting point for the string. Since a typical bridge saddle is only 3/32 inch to 1/8 inch wide, this task is delicate and involved.
To accomplish such modifications, a skilled luthier will first confirm that the basic saddle location is correct, and that some additional work will permit him to accurately set the intonation for each string. He may then take a file and slightly flatten the top of the existing saddle. If the original saddle location is wrong, the luthier fills the saddle slot and cuts a new one.
The luthier will then typically determine the preferred intonation point for each string as follows. A short length of guitar string of approximately 0.020-inch diameter has a right angle bend placed therein approximately 1/4 inch from the end of the string. The luthier can then slip this 1/4-inch long by 0.020-inch diameter wire under the string which is to be adjusted. Although this minutely raises the action height of the string, it is not sufficient to be noticeable. The luthier moves this wire toward the front, i.e., the neck end, or back of the saddle and compares the harmonic at the twelfth fret with the fretted tone at that point. Moving the wire segment back increases the length of the string, and causes the fretted note to be flatter in pitch. Once the harmonic and fretted note agree, the luthier marks the saddle to indicate the correct location of the support point, and then moves his bent wire to the next string and repeats the process.
Once the preferred intonation points for all of the strings have been marked on the top surface of the saddle, the saddle is removed from the guitar and placed in a vise. The luthier then uses a small file to notch excess material away from the marked locations. When this task is completed, the saddle is replaced and the instrument is tuned. This is a time-consuming and expensive procedure.
Another feature of acoustic guitars which is problematic is the adjustment of volume of individual string output on guitars which have electric pickups for use with an amplifier. The type of pickup most commonly used with hollow-bodied acoustic guitars is one utilizing piezo-electric transducers. In conventional piezo-electric pickups, the spacing of the individual crystals or transducer elements is predetermined by the manufacturer. Unfortunately, this spacing rarely, if ever, coincides with the actual string spacing of the instrument. When this happens, it is quite likely that the string output of the instrument will be uneven. Today's players are not fond of this, and luthiers employ many time-consuming and frustrating tricks to equalize this output. In addition, the different angles of the strings across the top of the saddle, as well as their relative masses, may also cause the output to vary. The player may be forced to vary his string gauges to get equal output from his pickup.
Thus there is a need for a bridge saddle and pickup design which will allow easy adjustment of the intonation point of individual strings, and which will allow adjustment of the relative outputs of strings when utilized with an electric pickup. The present invention addresses each of these needs, both individually and in combination.